Organic Chemistry I (Quiz 3)

Front 1

Which of the following alkenes exhibit E,Z-isomerism?
I. CH3CH=CHCH2CH3
II. (CH3)2C=CHCH3
III. CH3CH2CH=CHBr
IV. H2C=CHCH2CH(CH3)2

Back 1

Only I and III have different substituents attached to the alkene carbons. The reaction is concerted.

Front 2

Describe what happens in the E2 mechanism.

Back 2

The base attacks and then the leaving group departs in the same step.

Front 3

Describe what happens in the E1 mechanism.

Back 3

The leaving group departs in the first step. The base attacks in the second step. The reaction is not concerted.

Front 4

Carbon-carbon double bonds do not freely rotate like carbon-carbon single bonds. Why?

Back 4

Overlap of the two 2p orbitals of the pi bond would be lost. Pi overlap of p orbitals is required to generate a double bond. Rotating a pi bond would cause the overlap to disappear thereby breaking the double bond.

Front 5

How many isomeric alkenes of formula C4H8, including stereoisomers, are possible?

Back 5

4

Front 6

Which of the following alkenes exhibit E,Z-isomerism?
I. CH3CH=CHCH2CH3
II. (CH3)2C=CHCH3
III. CH3CH2CH=CHBr
IV. H2C=CHCH2CH(CH3)2

Back 6

Only I and III have different substituents attached to the alkene carbons

Front 7

Which of the following alkenes exhibit E,Z-isomerism?
I. 1-chloropropene
II. 2-chloropropene
III. 3-chloropropene

Back 7

Only I has different substituents attached to the alkene carbons.

Front 8

What is the major product of the acid-catalyzed dehydration of 2-methylpentan-2-ol (CH3C(CH3)(OH) CH2CH2CH3 )?

Back 8

2-methylpent-2-ene
The intermediate in this mechanism is the ionization of the protonated OH group to give a tertiary carbocation.

Front 9

Which alcohol would undergo acid-catalyzed dehydration most readily?

Back 9

1-methylcyclohexanol

like other E1 reaciton alcohol dehydration follows an order of reactivity that reflects carbocation stability: 3 alcohol react faster than 2 alcohols which is fast than 1
pg 314

Front 10

What is the slow, rate-determining step, in the acid-catalyzed dehydration of 2-methylbutan-2-ol (CH3C(CH3)(OH) CH2CH3 ?

Back 10

loss of water from the oxonium ion to form a carbocation

Front 11

Which of the following cannot undergo an E2 reaction?
I. 1-(bromomethyl)-1-methylcyclohexane
II. 1-bromo-1,2-dimethylcyclohexane
III. 1-(bromomethyl)-2-methylcyclohexane

Back 11

only I. There must be a hydrogen attached to the adjacent carbon in the dehydrohalogenation reaction to form an alkene.

Front 12

Which would be the best method for converting Ph–CHBr–CHBr–Ph to Ph–CH=CH–Ph (where Ph represents an aromatic, benzene, ring)?

Back 12

NaI, acetone. Dehalogenation using NaI in acetone would produce the indicated product.
section 7-9 D

Front 13

Guanine is one of the “nitrogenous bases” that form the letters of the genetic code. It has the molecular formula C5H5N5O When a sample of guanine is completely reacted with hydrogen gas and a Raney nickel catalyst, a compound with the formula C5H13N5O results. How many pi bonds and rings are in guanine?

Back 13

Pi bonds ____4______ Rings _____2______

Front 14

A newly isolated natural product was found to have the molecular formula C15H28O2. By hydrogenating a sample of the compound, it was determined to possess one pi bond. How many rings are present in the compound?

Back 14

1

Front 15

Which alkene will not rearrange in the course of an electrophilic addition?
a) 3,3-dimethyl-1-butene b) 3-ethylcyclohexene c) 3-methyl-2-hexene d) vinylcyclopentane

Back 15

c) 3-methyl-2-hexene

Front 16

The Simmons-Smith reaction involves an intermediate that is a
a) cyclic cation b) a carbanion
c) a carbenoid d) a radical

Back 16

c) a carbenoid

Front 17

Which of the following alkyl chlorides will undergo SN1 reaction most readily?
a) 1-chloro-4-methylpentane
b) 2-chloro-4-methylpentane
c) 2-chloro-3-methylpentane
d) 3-chloro-2-methylpentane
e) 2-chloro-2-methylpentane

Back 17

e) 2-chloro-2-methylpentane

Front 18

) When (Z)-3,4-dimethyl-3-hexene is reacted with hydrogen gas and a Raney nickel catalyst, what
product(s) will form?
a) a meso form
b) a racemic mixture
c) an optically active solution
d) a mixture that contains no chiral carbons

Back 18

a) a meso form

Front 19

) Which of the following species is the least nucleophilic?
a) H2O b) BF3 c) (CH3)3N d) CH3O- e) CN-

Back 19

b) BF3 or a) H2O

Front 20

Dehydration of an alcohol is essentially what type of reaction
a) E1 b) E2 c) SN1 d) SN2
e) electrophilic addition

Back 20

a) E1

Front 21

Which of the following is the best reaction to use to accomplish an anti-Markovnikov addition of water to an alkene?
a) water + dilute acid
b) halogenation
c) hydroboration-oxidation
d) oxymercuration-demercuration
e) catalytic hydrogenation

Back 21

c) hydroboration-oxidation

Front 22

Which one of the following cyclic alkenes can actually exist as cis and trans geometric isomers?

a.cyclobutene
b.cyclopentene
c.cyclohexene
d.cycloheptene
e.cyclooctene

Back 22

For cycloalkenes smaller than cyclooctene, the trans-isomer is not stable due to the large ring strain.

Front 23

Which of the following statements concerning the ring strain in cyclopropene is correct?

a. The C–C=C angle is reduced by 30 ° compared to its normal value in propene.
b. The C–C=C angle is reduced by 40 ° compared to its normal value in propene.
c. The C–C=C angle is reduced by 50 ° compared to its normal value in propene.
d. The C–C=C angle is reduced by 60 ° compared to its normal value in propene.
e. The C–C=C angle is reduced by 70 ° compared to its normal value in propene.

Back 23

The C–C=C angle is reduced by 60 ° compared to its normal value in propene. An sp2 carbon prefers 120° bond angles, while the cyclopropene ring enforces a bond angle of 60°.

Front 24

How many of the following five 1-alkenes—propene, butene, pentene, hexene, and heptene—are liquid at room temperature?

a. 1
b. 2
c. 3
d. 4
e. 5

Back 24

3. Propene and butene are gases with boiling points of -47 °C and -6 °C, respectively. All of the higher 1-alkenes are liquids at room temperature.

Front 25

The boiling point of trans-dichloroethene is 48 °C. Which number best approximates the boiling point of cis-dichloroethene?

a. 36 °C
b. 42 °C
c. 48 °C
d. 54 °C
e. 60 °C

Back 25

60 °C. The cis-isomer has a dipole moment, so it will have a higher boiling point than the trans-isomer.

Front 26

Which one of the following compounds has the largest dipole moment?

a. chloroethene
b. trans-1,2-dichloroethene
c. cis-1,2-dichloroethene
d. trichloroethene
e. tetrachloroethene

Back 26

cis-1,2-dichloroethene

Front 27

Consider the dehydrohalogenation of 2-bromo-2-methylbutane with ethoxide and t-butoxide. Which of the following statements is true?

a. Zaitsev product is the major product in both cases.
b. Hofmann product is the major product in both cases.
c. Ethoxide gives more Zaitsev products , tert-butoxide give less Hofmann product.
d. Ethoxide gives more Zaitsev products, tert-butoxide gives less Zaitsev product.

Back 27

Ethoxide gives more Zaitsev products, tert-butoxide gives less Zaitsev product. Smaller bases are able to remove the most hindered proton to give the more stable Zaitsev product. A bulky base, like tert-butoxide, has difficulty removing the more hindered proton, so more of the Hofmann product is formed.

Front 28

What conditions are best for the dehalogenation of vicinal dibromides?

a. Ag2O in acetone
b. NaI in hydrochloric acid
c. NaOH and heat
d. Na, NH3
e. heat and catalyst
f. NaI in acetone

Back 28

NaI in acetone

Front 29

Aside from concentrated sulfuric acid, what other strong acid is employed in the dehydration of alcohols?

a. concentrated hydrochloric acid
b. concentrated acetic acid
c. concentrated phosphoric acid
d. concentrated acetone
e. concentrated chromic acid

Back 29

concentrated phosphoric acid

Front 30

In the dehydration of an alcohol with concentrated sulfuric acid, which reaction step is the rate-limiting step?

a. protonation of alcohol
b. elimination of water from protonated alcohol
c. unimolecular elimination of hydroxide from alcohol
d. elimination of proton

Back 30

elimination of water from protonated alcohol
Protonation of an alcohol is fast and exothermic. Elimination of water produces an unstable carbocation. This is not a favorable reaction, so it proceeds slowly.

Front 31

Which relations correctly describe the thermodynamics of the dehydrogenation of butane?

a. ΔH > 0 and ΔS > 0
b. ΔH < 0 and ΔS < 0
c. ΔH > 0 and ΔS < 0
d. ΔH < 0 and ΔS > 0
e. ΔH about 0 and ΔS > 0

Back 31

ΔH > 0 and ΔS > 0
This reaction is endothermic and does not proceed at room temperature. Since 1 molecule of butane gives 1 molecule of butene and 1 molecule of hydrogen, the ΔS > 0. At high temperatures the ΔS term is large enough that the ΔG is negative and the reaction proceeds.

Front 32

The following four molecules all are "isoelectronic" with ethene: H2C=O, H2C=NH, HN=NH, and NH=O. Isoelectronic means that the molecules have the same numbers of electrons in the same types of orbitals. Which one of the four molecules can form geometric isomers?

a. H2C=O
b. H2C=NH
c. HN=NH
d. HN=O
e. None of these exists as geometric isomers.

Back 32

HN=NH
The hydrogen and nonbonded pair of electrons on each nitrogen count as two different substituents on each atom of the double bond, which gives two geometric isomers.

Front 33

What is the approximate energy of a pi bond in ethene? See Table 4-2 for relevant bond dissociation energies.

a. 238 kJ/mol
b. 251 kJ/mol
c. 264 kJ/mol
d. 347 kJ/mol
e. 611 kJ/mol

Back 33

264 kJ/mol

Front 34

How long is the C=C double bond in ethene?

a. 1.20 Å
b. 1.33 Å
c. 1.44 Å
d. 1.54 Å
e. 2.10 Å

Back 34

1.33 Å
This is the length of a C=C bond.

Front 35

What is the hybridization of the C-atom in ethene?

a. sp3
b. sp2
c. sp
d. pure s
e. pure p

Back 35

sp2

An sp3-hybridized carbon cannot form any pi bonds because it has no p orbitals.

Front 36

What causes the rotational barrier in alkenes?

a. C(sp3)-C(sp3) overlap
b. C(sp2)-C(sp2) overlap
c. C(sp)-C(sp) overlap
d. C(p)-C(p) overlap
e. C(sp2)-C(p) overlap

Back 36

C(p)-C(p) overlap

Front 37

What is the general molecular formula for cyclic alkenes?

a. CnH2n-2
b. CnH2n
c. CnH2n+2
d. CnH2n+4
e. CnH2n+6

Back 37

CnH2n-2

CnH2n+2:This is the formula of a hydrocarbon with no elements of unsaturation.

Front 38

What is the number of elements of unsaturation in the molecule with the formula C8H16O2?

a. 0
b. 1
c. 2
d. 3
e. 4

Back 38

1
Oxygen can be ignored when determining the number of elements of unsaturation. The molecule has two fewer hydrogens than a fully saturated hydrocarbon.

Front 39

Name the hydrocarbon CH3-CH=CH-CH2CH2CH3 using IUPAC nomenclature.

a. hex-1-ene
b. hexene-2
c. hex-2-ene
d. pent-2-ene
e. hex-2-ane

Back 39

hex-2-ene

hex-1-ene:This name says that the double bond starts at carbon 1.

Front 40

Which formula correctly shows 2-bromo-4-ethyl-7-methyloct-4-ene?

a. CH3-CHBr-CH2-CH=C(C2H5)-CH2-CH(CH3)2
b. (CH3)2CH-CH=CH-CH(C2H5)-CH2-CH2-CH3
c. (CH3)2CH-CH2-CH=C(C2H5)-CH2-CHBr-CH3
d. (CH3)2CH-CH2-CH=CH-CH2-CH2-CH3
e. (CH3)2CH-CH2-CH2-CH(C2H5)-CH2-CHBr-CH3

Back 40

(CH3)2CH-CH2-CH=C(C2H5)-CH2-CHBr-CH3

Front 41

How many rings and double bonds are there in 2-phenylcyclopenta-1,3-diene?

a. 1 ring, 4 double bonds
b. 1 ring, 5 double bonds
c. 1 ring, 6 double bonds
d. 2 rings, 4 double bonds
e. 2 rings, 5 double bonds

Back 41

2 rings, 5 double bonds
A phenyl substituent has 1 ring and 3 double bonds. The cyclopentadiene group has 1 ring and 2 double bonds.

Front 42

Which of the following compounds cannot exist as cis/trans isomers?

a. CH3–CH=CH–C2H5
b. H2C=CH–C2H5
c. Cl–CH=CH–Cl
d. Cl–CH=CH–Br
e. Cl–CH=CH–CH3

Back 42

H2C=CH–C2H5
For an alkene to have cis/trans isomers, it must have two different substituents at each carbon of the alkene. A cis alkene has the major substituents on the same side of the alkene, while a trans alkene has them on opposite sides.

Front 43

Which olefin is the building block of the polymer "PVC"?

a. ethene
b. chloroethene
c. 1,2-dichloroethene
d. 1,1-dichloroethene
e. 1,1,2,2-tetrachloroethene

Back 43

chloroethene
PVC = poly(vinyl chloride)
Vinyl chloride = chloroethene

Front 44

Identify the alkene with the lowest molar heat of hydrogenation.

a. ethene
b. propene
c. 2,3-dimethylbut-1-ene
d. transpent-2-ene
e. 2,3-dimethylbut-2-ene

Back 44

2,3-dimethylbut-2-ene
Alkyl substituents stabilize alkenes, so the most substituted alkene will have the lowest heat of hydrogenation.

Front 45

Dehydration of alcohols commonly utilizes:

a. NaOH
b. Br2
c. SOCl2
d. Zn
e. H2SO4

Back 45

H2SO4
Correct, dehydrations are acid catalyzed.

Front 46

The loss of a halide atom to generate an alkene is known as:

a. dehydration.
b. Hofmann elimination.
c. hydrogenation.
d. dehalogenation.
e. dehydrohalogenation.

Back 46

dehydrohalogenation.
While dehalogenation involves halogen atoms, the product is a diatomic halogen species. Dehydrohalogenation involves the formation of a hydrogen halide.

Front 47

Which one of the following cyclic alkenes can actually exist as cis and trans geometric isomers?

a. cyclobutene
b. cyclopentene
c. cyclohexene
d. cycloheptene
e. cyclooctene

Back 47

cyclooctene

For cycloalkenes smaller than cyclooctene, the trans-isomer is not stable due to the large ring strain.

Front 48

Which of the following statements concerning the ring strain in cyclopropene is correct?

a. The C–C=C angle is reduced by 30 ° compared to its normal value in propene.
b. The C–C=C angle is reduced by 40 ° compared to its normal value in propene.
c. The C–C=C angle is reduced by 50 ° compared to its normal value in propene.
d. The C–C=C angle is reduced by 60 ° compared to its normal value in propene.
e. The C–C=C angle is reduced by 70 ° compared to its normal value in propene.

Back 48

d. The C–C=C angle is reduced by 60 ° compared to its normal value in propene.

An sp2 carbon prefers 120° bond angles, while the cyclopropene ring enforces a bond angle of 60°.

Look at slide 7-34

Front 49

How many of the following five 1-alkenes—propene, butene, pentene, hexene, and heptene—are liquid at room temperature?

a. 1
b. 2
c. 3
d. 4
e. 5

Back 49

3

Propene and butene are gases with boiling points of -47 °C and -6 °C, respectively. All of the higher 1-alkenes are liquids at room temperature.

table 7-2 pg 303

Front 50

The boiling point of trans-dichloroethene is 48 °C. Which number best approximates the boiling point of cis-dichloroethene?

a. 36 °C
b. 42 °C
c. 48 °C
d. 54 °C
e. 60 °C

Back 50

60 °C
The isomer with the dipole moment boils at a higher temperature.
The cis-isomer has a dipole moment, so it will have a higher boiling point than the trans-isomer.

Front 51

Which one of the following compounds has the largest dipole moment?

a. chloroethene
b. trans-1,2-dichloroethene
c. cis-1,2-dichloroethene
d. trichloroethene
e. tetrachloroethene

Back 51

cis-1,2-dichloroethene

The net bond dipoles of the two C–Cl bonds are additive

Front 52

Consider the dehydrohalogenation of 2-bromo-2-methylbutane with ethoxide and t-butoxide. Which of the following statements is true?

a. Zaitsev product is the major product in both cases.
b. Hofmann product is the major product in both cases.
c. Ethoxide gives more Zaitsev products , tert-butoxide give less Hofmann product.
d. Ethoxide gives more Zaitsev products, tert-butoxide gives less Zaitsev product.

Back 52

Ethoxide gives more Zaitsev products, tert-butoxide gives less Zaitsev product.
Smaller bases are able to remove the most hindered proton to give the more stable Zaitsev product. A bulky base, like tert-butoxide, has difficulty removing the more hindered proton, so more of the Hofmann product is formed.

Front 53

What conditions are best for the dehalogenation of vicinal dibromides?

a. Ag2O in acetone
b. NaI in hydrochloric acid
c. NaOH and heat
d. Na, NH3
e. heat and catalyst
f. NaI in acetone

Back 53

NaI in acetone

see section 7-9D

Front 54

Aside from concentrated sulfuric acid, what other strong acid is employed in the dehydration of alcohols?

a. concentrated hydrochloric acid
b. concentrated acetic acid
c. concentrated phosphoric acid
d. concentrated acetone
e. concentrated chromic acid

Back 54

c. concentrated phosphoric acid

Front 55

In the dehydration of an alcohol with concentrated sulfuric acid, which reaction step is the rate-limiting step?

a. protonation of alcohol
b. elimination of water from protonated alcohol
c. unimolecular elimination of hydroxide from alcohol
d. elimination of proton

Back 55

elimination of water from protonated alcohol

Elimination of water produces an unstable carbocation. This is not a favorable reaction, so it proceeds slowly.

Front 56

Which relations correctly describe the thermodynamics of the dehydrogenation of butane?

a. ΔH > 0 and ΔS > 0
b. ΔH < 0 and ΔS < 0
c. ΔH > 0 and ΔS < 0
d. ΔH < 0 and ΔS > 0
e. ΔH about 0 and ΔS > 0

Back 56

ΔH > 0 and ΔS > 0

This reaction is endothermic and does not proceed at room temperature. Since 1 molecule of butane gives 1 molecule of butene and 1 molecule of hydrogen, the ΔS > 0. At high temperatures the ΔS term is large enough that the ΔG is negative and the reaction proceeds.

Front 57

The following four molecules all are "isoelectronic" with ethene: H2C=O, H2C=NH, HN=NH, and NH=O. Isoelectronic means that the molecules have the same numbers of electrons in the same types of orbitals. Which one of the four molecules can form geometric isomers?

a. H2C=O
b. H2C=NH
c. HN=NH
d. HN=O
e. None of these exists as geometric isomers.

Back 57

HN=NH

There must be two different substituents on each atom of the double bond to have geometric isomers.

Front 58

How long is the C=C double bond in ethene?

Back 58

1.33 Å

Front 59

What is the hybridization of the C-atom in ethene?

Back 59

sp2

Front 60

What causes the rotational barrier in alkenes?

Back 60

C(p)-C(p) overlap

Front 61

What is the general molecular formula for cyclic alkenes?

Back 61

CnH2n-2

This formula accounts for two elements of unsaturation, one from the ring and one from the alkene.

Front 62

What is the number of elements of unsaturation in the molecule with the formula C8H16O2?

Back 62

1

Oxygen can be ignored when determining the number of elements of unsaturation. The molecule has two fewer hydrogens than a fully saturated hydrocarbon.

Front 63

Name the hydrocarbon CH3-CH=CH-CH2CH2CH3 using IUPAC nomenclature.

Back 63

hex-2-ene

This is a six-carbon chain with the root name hex- and a carbon-carbon double bond at the 2- position.

Front 64

Which formula correctly shows 2-bromo-4-ethyl-7-methyloct-4-ene?

a. CH3-CHBr-CH2-CH=C(C2H5)-CH2-CH(CH3)2
b. (CH3)2CH-CH=CH-CH(C2H5)-CH2-CH2-CH3
c. (CH3)2CH-CH2-CH=C(C2H5)-CH2-CHBr-CH3
d. (CH3)2CH-CH2-CH=CH-CH2-CH2-CH3
e. (CH3)2CH-CH2-CH2-CH(C2H5)-CH2-CHBr-CH3

Back 64

c. (CH3)2CH-CH2-CH=C(C2H5)-CH2-CHBr-CH3

Front 65

How many rings and double bonds are there in 2-phenylcyclopenta-1,3-diene?

a. 1 ring, 4 double bonds
b. 1 ring, 5 double bonds
c. 1 ring, 6 double bonds
d. 2 rings, 4 double bonds
e. 2 rings, 5 double bonds

Back 65

2 rings, 5 double bonds

A phenyl substituent has 1 ring and 3 double bonds. The cyclopentadiene group has 1 ring and 2 double bonds.

Front 66

Which of the following compounds cannot exist as cis/trans isomers?

a. CH3–CH=CH–C2H5
b. H2C=CH–C2H5
c. Cl–CH=CH–Cl
d. Cl–CH=CH–Br
e. Cl–CH=CH–CH3

Back 66

H2C=CH–C2H5

For an alkene to have cis/trans isomers, it must have two different substituents at each carbon of the alkene.

Front 67

Open Hint for Question 22 in a new window Which olefin is the building block of the polymer "PVC"?

a. ethene
b. chloroethene
c. 1,2-dichloroethene
d. 1,1-dichloroethene
e. 1,1,2,2-tetrachloroethene

Back 67

chloroethene

PVC = poly(vinyl chloride)
Vinyl chloride = chloroethene

Front 68

Identify the alkene with the lowest molar heat of hydrogenation.

a. ethene
b. propene
c. 2,3-dimethylbut-1-ene
d. transpent-2-ene
e. 2,3-dimethylbut-2-ene

Back 68

2,3-dimethylbut-2-ene

Alkyl substituents stabilize alkenes, so the most substituted alkene will have the lowest heat of hydrogenation.

Front 69

Dehydration of alcohols commonly utilizes:

a. NaOH
b. Br2
c. SOCl2
d. Zn
e. H2SO4

Back 69

H2SO4

Front 70

The loss of a halide atom to generate an alkene is known as:

a. dehydration.
b. Hofmann elimination.
c. hydrogenation.
d. dehalogenation.
e. dehydrohalogenation.

Back 70

dehydrohalogenation.

While dehalogenation involves halogen atoms, the product is a diatomic halogen species. Dehydrohalogenation involves the formation of a hydrogen halide.